The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention pertains to the field of propellants and explosives, more particularly to hydroxy terminated polybutadiene (HTPB) based binders for energetic materials, and most particularly to hydroxy functionalized polybutadiene (HFPB) based binders for energetic materials that possess improved compatibility with energetic plasticizers and are chemically degradable.
2. Brief Description of the Prior Art
Many solid propellant and explosive binders used today are reaction products of HTPB prepolymers. This is due to HTPB binders having excellent mechanical properties as discussed further below. These binders are often diluted with up to 40% inert plasticizers. Inert plasticizers do not carry energetic groups and their main purpose is to improve processability and the flexibility of the binder at low temperatures. However, these inert binders not only reduce performance of the propellant or explosive, but also require very high levels of oxidizer to effect complete combustion. Therefore, the use of energetic plasticizers is attractive in the preparation of solid propellants and explosives. The major problem with the use of energetic plasticizers with HTPB based prepolymers is the lack of compatibility. This is because the common energetic plasticizers, mainly high energy nitrato- or nitro-compounds, are not soluble to any significant extent in HTPB prepolymers. The major focus to solving this problem has been the development of new energetic plasticizers that are more compatible with HTPB prepolymers. One example is U.S. Pat. No. 5,578,789 that discloses an energetic plasticizer that is a polybutadiene compatible nitrato-derivative of aliphatic hydrocarbons. However, none of these new energetic plasticizers have overcome the performance or cost issues necessary to become widely used. In view of the above discussion, it is desired to produce a new polybutadiene based polymer that is more compatible with common energetic plasticizers used in solid propellant and explosive formulations.
As noted above, HTPB based binders are widely used due to good mechanical properties and long shelf life. This is the result of the insoluble binder network formed from the HTPB prepolymer. One drawback of such an insoluble binder is that it does not allow for the reclamation of the energetic ingredients and hardware after the shelf life of the propellant or explosive has expired. Therefore, it is also desired to produce a polybutadiene based binder that is chemically degradable, in particular by hydrolysis, solvolysis, or similar chemical reactions.
The present invention is a modified HFPB polymer for use in propellants and explosives that is chemically degradable and also is compatible with commonly used energetic plasticizers.
Accordingly it is an object of this invention to provide a modified polybutadiene polymer that can be used in a binder for explosives and propellants.
It is a further object of this invention to provide a polybutadiene type polymer that is compatible with energetic plasticizers commonly used in propellant and explosive formulations.
It is yet a further object of this invention to provide a polybutadiene type polymer that can be used in a binder that is chemically degradable.
This invention accomplishes these objectives and other needs related to polybutadiene based polymers used for explosive and propellant binders by providing a HFPB polymer that contains ester linkages formed in the backbone of the polymer from dicarboxylic acids containing either oxymethylene or oxyethylene moeities. The ester and ether linkages change the polarity of the polybutadiene to make it compatible with polar energetic plasticizers. The ester linkages along with either the oxymethylene or oxyethylene moeities make the polymer degradable by basic or acidic polar liquids while still maintaining the structural integrity necessary for a polybutadiene type binder. The invention also includes a process for producing the HFPB polymer described herein.